Our invention relates to an amplifier, and particularly to an improved amplifier for providing relatively high power amplification over a relatively broad range of frequencies.
In some commercial or industrial applications, relatively high power amplification over a relatively wide range of frequencies is required. For example, in industrial carrier systems operating on commercial power lines, such amplifiers may be required to produce as much as 100 or 200 watts of output power over a frequency range between 8 and 500 kilohertz. Because of the reliability requirements placed on such amplifiers, proper operation of the amplifiers is highly desirable, if not absolutely necessary.
Accordingly, a primary object of our invention is to provide a new and improved amplifier that can produce a relatively high output power over a relatively wide range of frequencies.
A relatively specific object of our invention is to provide a new and reliable improved amplifier that is capable of producing output powers in the order of 200 watts over a frequency range between 8 and 500 kilohertz.
A transistorized power amplifier which could be used in the applications mentioned above is described in U.S. Pat. No. 3,596,199 granted July 27, 1971. However, the amplifier described in that patent is primarily designed for high quality audio sound systems. It will be appreciated that such sound systems do not need the reliability and the output power that are required in applications such as described above. Specifically, while the amplifier described in that patent does provide power amplification and protection in the event of overload or overdrive, it does not have an arrangement or feature for reliably restoring the amplifier to normal operation after the overload or overdrive is removed. Restoral of that amplifier depends upon the momentary removal of the input signal, a condition which is very likely to occur in audio sound systems. However, in commercial or industrial applications such as carrier systems, and particularly power line relaying systems, removal of the signal is not likely to occur and might, in fact, be very serious or even disastrous.
Accordingly, another object of our invention is to provide a new and improved amplifier having the desired protection features of known amplifiers, but having a further new and improved feature of being reliably self-restoring once the overload or overdrive condition is removed.
Another relatively specific object of our invention is to provide a new amplifier which has protection circuits for overload or overdrive conditions, and which restore the amplifier to operation once the overload or overdrive condition is removed, even though normal input drive signals may still be applied.